Navien Tankless Hot Water Heater Leaking: A Pro'S Step-By-Step

There are few things that cause a homeowner’s heart to sink faster than the sight of water pooling around a major appliance. When you discover your Navien tankless hot water heater leaking, it’s easy to feel a surge of panic. You rely on that unit for endless hot showers and clean dishes, and a leak feels like a major, expensive problem.

Don’t worry—we’ve got your back. As HVACR professionals, we see this issue all the time. The good news is that not every leak spells disaster. Many are caused by simple, fixable issues that a determined homeowner can safely identify.

We promise this guide will walk you through the exact steps a technician takes to find the source of the leak. We’ll preview how to safely assess the situation, identify the most common culprits from loose fittings to pressure valve issues, and help you understand when it’s safe to DIY and when it’s time to call in a certified pro. Let’s get that leak sorted out.

First Steps: What to Do Immediately When You Find a Leak

Before you start investigating, your first priority is safety and damage control. Water and electricity (or gas) are a dangerous combination. Follow these steps in order before doing anything else.

Shut Off the Power or Gas. For electric models, find the corresponding breaker in your electrical panel and switch it off. For gas models, locate the gas shutoff valve on the line leading to the heater (it usually has a red or yellow handle) and turn it perpendicular to the pipe to close it.
Turn Off the Water Supply. Your Navien unit will have a cold water inlet valve. It’s typically a T-shaped handle. Turn this handle so it’s perpendicular to the water pipe. This stops more water from entering the heater.
Clean Up the Area. Mop or towel up any standing water to prevent water damage and create a safe, slip-free workspace for your inspection.

Once you’ve contained the situation, you can safely begin your diagnosis. Taking these initial steps protects you, your home, and your water heater.

Pinpointing the Source: Common Problems with Navien Tankless Hot Water Heater Leaking

A leak can come from several places. Working methodically from the most likely to the least likely source will help you find the problem faster. Grab a flashlight and a dry paper towel—the paper towel will show moisture instantly when you touch it to a fitting.

Water Connection Leaks (The Most Common Culprit)

The vast majority of leaks we find are right at the water connections. Over time, vibrations and temperature changes can cause fittings to loosen slightly.

Hot and Cold Water Lines: Check the threaded connections where your home’s plumbing attaches to the hot and cold water ports on the bottom of the unit. Dab the paper towel around the base of each fitting.
Isolation Valves: Your Navien was installed with isolation valves (service valves) for maintenance. Check for drips around the valve stems and connection points.
The Fix: If you find a drip here, you can often solve it by gently tightening the connection with a wrench. Give it a quarter-turn—do not overtighten, as this can crack the fitting and create a much bigger problem.

Pressure Relief Valve (PRV) Discharge

The Temperature and Pressure Relief (TPR or PRV) valve is a critical safety device. It’s designed to open and release water if the pressure or temperature inside the unit gets dangerously high. A dripping PRV is a major warning sign.

Location: It’s a brass valve with a small lever on top, usually connected to a pipe that runs down toward the floor.
Why it leaks: It could be a sign of excessive pressure in your home’s plumbing, a failing expansion tank, or a faulty valve. Sometimes, a small piece of sediment can get stuck in the valve seat, preventing it from closing completely.
The Fix: This is often a job for a professional. High pressure is a serious issue. A technician can test your home’s water pressure and diagnose the root cause. Never, ever cap or plug a leaking PRV.

Condensate Line Issues

High-efficiency condensing units like most Navien models produce acidic condensate (water) as a byproduct of combustion. This water is drained away through a plastic tube.

The Problem: If this drain line becomes clogged with debris or freezes in the winter, the water will back up and leak from the unit, often from the bottom casing.
The Fix: Check that the condensate line is clear and has a proper downward slope. You may be able to clear a simple clog yourself by disconnecting the tube and flushing it out. This is a key part of any navien tankless hot water heater leaking care guide.

Internal Leaks (When to Call a Pro)

If you’ve checked all the external connections and can see water dripping from inside the main casing of the unit itself, the problem is internal. This is not a DIY situation.

An internal leak could be from a pinhole in the heat exchanger, a cracked O-ring on an internal component, or a failed sensor. Attempting to fix this without proper training can cause irreparable damage to the unit and void your warranty.

If you suspect an internal leak, your next and only step should be to call a Navien-certified technician. This is one of the most important navien tankless hot water heater leaking tips we can offer.

Your Navien Tankless Hot Water Heater Leaking Guide: A Step-by-Step Inspection

Ready to put on your detective hat? Here is a simple, safe inspection process to follow. Remember, power and water are off!

Start with a Visual Scan. With your flashlight, look for the obvious signs: active dripping, white or green crusty buildup (mineral deposits), or rust trails.
The Paper Towel Test. Start at the top and work your way down. Touch a dry paper towel to every connection point:
- Where the cold water line enters the unit.
- Where the hot water line exits the unit.
- Around the base of the pressure relief valve.
- At the connections for the condensate drain line.
Check the Casing. Carefully inspect the seams and bottom of the unit’s outer casing. Is water seeping from inside? This points to an internal issue.
Listen Closely. Before you found the leak, did you hear any unusual hissing or dripping sounds? This can provide a clue to the leak’s location.

Following this simple how to navien tankless hot water heater leaking diagnostic process helps you isolate the problem without taking unnecessary risks.

Preventative Maintenance: Your Best Defense Against Future Leaks

The best way to handle a leak is to prevent it from ever happening. Regular maintenance is crucial for the longevity and efficiency of your Navien unit. This is one of the most important navien tankless hot water heater leaking best practices.

Annual Descaling: Hard water minerals build up inside the heat exchanger, which can cause corrosion and eventually lead to leaks. Flushing (descaling) your unit once a year with a vinegar solution is the single most important maintenance task.
Inspect Connections: During your annual flush, take a moment to visually inspect all the water connections for any signs of corrosion or slow drips.
Clean the Inlet Filter: The cold water inlet has a small screen filter to catch sediment. Cleaning this annually prevents blockages that can stress the system.

The Eco-Friendly Advantage: Why Fixing Leaks Matters

Fixing a leak isn’t just about preventing water damage. It’s also a key part of maintaining your system’s efficiency. A slow, steady drip of hot water is a constant drain on energy as the unit fires up unnecessarily to heat water that’s just going down the drain.

By addressing leaks promptly, you are practicing sustainable navien tankless hot water heater leaking management. You conserve water, save energy, and reduce your utility bills—a win for your wallet and the environment. This is one of the key benefits of navien tankless hot water heater leaking repair: protecting your investment and the planet.

Frequently Asked Questions About a Leaking Navien Water Heater

Why is my Navien pressure relief valve leaking?

A leaking PRV is typically caused by one of three things: excessively high household water pressure (over 80 PSI), a faulty or failed expansion tank, or debris stuck in the valve itself. It’s a safety system doing its job, and the underlying cause needs to be addressed by a professional.

Can I fix a small leak on my Navien heater myself?

It depends on the source. If the leak is from a loose hot or cold water connection fitting, you can often fix it by gently tightening the nut with a wrench (a quarter-turn is usually enough). For any other leaks, especially from the PRV or from inside the unit’s casing, it is highly recommended to call a certified technician for safety and to protect your warranty.

How much does it cost to fix a leaking Navien tankless water heater?

The cost varies widely depending on the cause. Tightening a loose fitting might cost nothing if you do it yourself, or a minimum service call fee from a plumber ($150-$300). Replacing a faulty PRV could cost $250-$500. A major internal leak, such as a failed heat exchanger, can be much more expensive, potentially running over $1,500, though it may be covered under Navien’s warranty.

How often should I have my Navien unit serviced to prevent leaks?

We recommend professional service once a year. An annual service call should include a full inspection, cleaning of the inlet filters, and a system flush/descaling. This preventative maintenance is the best way to catch potential problems before they turn into damaging leaks.

Discovering a navien tankless hot water heater leaking can be stressful, but you are now equipped with the knowledge to tackle it calmly and safely. By carefully inspecting the connections, understanding the role of each component, and knowing your limits, you can often identify the source of the problem quickly.

Remember to always prioritize safety by shutting off the utilities first. For simple connection leaks, a gentle tightening might be all you need. For anything more complex, never hesitate to call in a qualified professional. Your Navien heater is a sophisticated piece of equipment, and proper care will ensure it provides you with safe, efficient, and endless hot water for years to come.

Stay safe and stay comfortable!

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David Clark

Founder & Lead HVAC Specialist at HVACRLY

David Clark is the founder of HVACrly and a certified HVAC specialist with 10+ years working on residential and light-commercial systems. He turns complex heating, cooling, ventilation, and refrigeration topics into clear, actionable guides focused on safety and energy efficiency. When he’s not on a service call, he’s testing tools and writing step-by-step tutorials.